1. Field of the Invention
The present invention relates to an electronic throttle control apparatus for controlling an electronic throttle valve which serves to adjust an amount of intake air in an internal combustion engine, and more particularly, it relates to an electronic throttle control apparatus which is able to cope with the time of abnormality of an electronic throttle valve angle detection sensor (hereinafter referred to simply as an “angle sensor”) which serves to detect an angle of the electronic throttle valve.
2. Description of the Related Art
In general, in an internal combustion engine mounted on a vehicle, etc., there has been used, as a throttle valve for adjusting an amount of intake air, an electronic throttle valve which is mechanically connected with an accelerator pedal which is operated by a driver, and there have been proposed a variety of kinds of electronic throttle control apparatuses for carrying out feedback control of an electronic throttle valve in accordance with detection information on the throttle angle of the throttle valve.
In this kind of electronic throttle control apparatus, it is constructed such that when a system abnormality such as a failure of an angle sensor has occurred, in order to ensure safety of the vehicle, the supply of electric power to a motor for driving the electronic throttle valve is interrupted so as to prevent the rotational speed of the internal combustion engine from being raised in an abrupt manner, and the electronic throttle valve is induced or guided to a predetermined intermediate degree of opening by means of an induction or guidance mechanism which functions at the time of abnormality.
However, in cases where a system abnormality has occurred in an open position of the electronic throttle valve, the electronic throttle valve is closed toward the intermediate degree of opening by means of the induction mechanism although the supply of electric power to the motor for driving the electronic throttle valve (hereinafter referred to simply as a “motor”) is interrupted, so the engine rotational speed of the internal combustion engine decreases in a rapid manner. As a result, a sudden deceleration of the vehicle may be caused, and in particular, in vehicles of light weight such as a two-wheeled motor vehicle, a sudden deceleration condition may result.
Accordingly, in recent years, there is also proposed an electronic throttle valve control apparatus in which in cases where a system abnormality has occurred, by putting the motor into a regenerative state, the speed at which the electronic throttle valve moves to the intermediate degree of opening is suppressed by means of the induction mechanism, so that a rapid decrease in the rotational speed of the internal combustion engine is thereby prevented (for example, see a first patent document).
However, in an electronic throttle valve control apparatus described in the first patent document, too, it is not possible to prevent a change in the actual angle of the electronic throttle valve (hereinafter referred to as the “actual throttle angle”) which is generated by the motor being controlled by the time when a system abnormality is detected.
In addition, a means for putting the motor into a regenerative state after a system abnormality is detected serves to hold the change of the actual throttle angle which has been generated by the time when the system abnormality is detected, so a sudden deceleration or sudden acceleration of the vehicle can be caused.
For example, in cases where the angle sensor becomes abnormal, in a period of time until the abnormality is detected, the motor is controlled by the use of angle information which is different from the actual throttle angle.
As a result, a sudden deceleration or a sudden acceleration of the vehicle will be caused due to the change of the actual throttle angle generated by the control of the motor until the time when the abnormality is detected, as well as the holding of an angular difference between a target throttle opening (target opening) and the actual throttle angle at the time of putting the motor into the regenerative state after the detection of abnormality.
As a measure against the above-mentioned sudden acceleration and deceleration, there has also been proposed a technique in which in order to suppress a change in an actual throttle angle generated by the time when a system abnormality is detected, a mechanical mechanism is provided which is connected with an accelerator pedal adapted to be operated by a driver, so that the degree of operating angle of an electronic throttle valve is restricted.
However, in cases where the mechanical mechanism connected with the accelerator pedal so as to restrict the degree of operating angle of the electronic throttle valve is used, even if the system of an electronic throttle control apparatus is in a normal state, the electronic throttle valve can not be controlled beyond the degree of operating angle thereof, because the degree of operating angle of the electronic throttle valve is restricted.
In addition, in the electronic throttle valve which has a restriction on the degree of operating angle thereof, there is also the problem that in cases where the driver abruptly operates the accelerator pedal to its closed side, the electronic throttle valve is closed in an abrupt manner, irrespective of the operating state of the internal combustion engine.
In this case, because the intake air to the internal combustion engine is interrupted or cut off rapidly, the fuel adhered to an intake manifold does not often burn, thus leading to the degradation of a three-way catalyst which is arranged in an exhaust system, as well as the deterioration of exhaust gas.
On the other hand, as stated above, in the case of adopting an electronic throttle valve which is not provided with a restriction mechanism mechanically connected with an accelerator pedal adapted to be operated by a driver, it becomes possible to carry out optimal fuel injection based on the condition of the accelerator pedal operated by the driver and the operating state of the internal combustion engine.
As described above, the suppression of the change of the actual throttle angle generated by the time when a system abnormality in the electronic throttle valve control apparatus is detected, and the abolition of the mechanical mechanism for restricting the degree of operating angle of the electronic throttle valve have a relation of trade-off, and hence, it is difficult to solve both of these problems at the same time.